No abstract

Mantle plumes upwelling beneath moving tectonic plates generate age-progressive chains of volcanos (hotspot chains) used to reconstruct plate motion. However, these hotspots appear to move relative to each other, implying that plumes are not laterally fixed. The lack of age constraints on long-lived, coeval hotspot chains hinders attempts to reconstruct plate motion and quantify relative plume motions. Here we provide 40Ar/39Ar ages for a newly identified long-lived mantle plume, which formed the Rurutu hotspot chain. By comparing the inter-hotspot distances between three Pacific hotspots, we show that Hawaii is unique in its strong, rapid southward motion from 60 to 50 Myrs ago, consistent with paleomagnetic observations. Conversely, the Rurutu and Louisville chains show little motion. Current geodynamic plume motion models can reproduce the first-order motions for these plumes, but only when each plume is rooted in the lowermost mantle.

No abstract

The existence of mantle plumes was first proposed in the 1970s to explain intra-plate, hotspot volcanism, yet owing to difficulties in resolving mantle upwellings with geophysical images and discrepancies in interpretations of geochemical and geochronological data, the origin, dynamics and composition of plumes and their links to plate tectonics are still contested. In this Review, we discuss progress in seismic imaging, mantle flow modelling, plate tectonic reconstructions and geochemical analyses that have led to a more detailed understanding of mantle plumes. Observations suggest plumes could be both thermal and chemical in nature, can attain complex and broad shapes, and that more than 18 plumes might be rooted in regions of the lowermost mantle. The case for a deep mantle origin is strengthened by the geochemistry of hotspot volcanoes that provide evidence for entrainment of deeply recycled subducted components, primordial m an tle domains and, potentially, materials from Earth's core. Deep mantle plumes often appear deflected by large-scale mantle flow, resulting in hotspot motions required to resolve past tectonic plate motions. Future research requires improvements in resolution of seismic tomography to better visualize deep mantle plume structures at smaller than 100-km scales. Concerted multi-proxy geochemical and dating efforts are also needed to better resolve spatiotemporal and chemical evolutions of long-lived mantle plumes.